The preparation of azo dye derivative  from " p- amino Salicylic acid " through preparation diazonium salt from aromatic amine followed by coupling reaction with (2,2,4,4-tetrahydroxybenzophenonto) was carried out to give (salicylic acid azo 2,2,4,4  tetrahydroxybenzophenon) using Dowex in the acidic form as a catalyst. The structure of azo dye produced by this reaction was assigned on the bases of spectral data (FT-IR) and (C.H.N.) analysis and the results obtained indicated the occurrence of the coupling reaction by the novel acidic catalyst.